1. Field of the Invention
The invention relates to a control apparatus of an internal combustion engine and a control method of an internal combustion engine.
2. Description of the Related Art
An internal combustion engine is known in which a plurality of cylinders of the internal combustion engine are divided into two groups. When the load on the internal combustion engine is less than a value for switching operation modes (hereinafter referred to as “operation mode switching value”), the internal combustion engine operates in a partial cylinder operation mode in which only one of the two cylinder groups is operated. When the load on the internal combustion engine is greater than the operation mode switching value, the internal combustion engine operates in a full cylinder operation mode in which both cylinder groups are operated. Accordingly, fuel consumption is reduced when operating under a low load while greater engine output is able to be ensured when operating under a high load.
Here, in consideration of fuel consumption, it is preferable to set the operation mode switching value as high as possible to increase the operating region in which the internal combustion engine operates in the partial cylinder operation mode as much as possible.
Japanese Patent Application Publication No. JP-A-8-105339 describes a related internal combustion engine. With this related internal combustion engine, when the load on the internal combustion engine is low when the internal combustion engine is to be operated in the partial cylinder operation mode, the internal combustion engine is operated in the partial cylinder operation mode with a lean air-fuel ratio. When the load on the internal combustion engine is high when the internal combustion engine is to be operated in the partial cylinder operation mode, the internal combustion engine is operated in the partial cylinder operation mode with the stoichiometric air-fuel ratio.
However, there is a limit as to just how much fuel consumption can be reduced when the air-fuel ratio is made rich in order to shift it from a lean air-fuel ratio to the stoichiometric air-fuel ratio.